1 Long before satellites and airplanes captured a view of our planet's surface, explorers were our only set of eyes. Through their travels they gave mapmakers information about oceans, new continents, and their coastlines. This is how our first reliable maps of Earth were made. Early explorers also noticed how the continental shorelines on both sides of the Atlantic Ocean appeared as if they fit together. They looked as if they were broken apart from a continental jigsaw puzzle. If you were to look at a world map, you may have noticed that the western coast of Africa appears to fit perfectly with the eastern coast of South America. Alfred Wegener also noticed this feature about our coastlines.2 Wegener was a German scientist who proposed the continental drift hypothesis in 1912. His hypothesis stated that our continents were once part of a single supercontinent. Wegener also stated that this supercontinent started breaking into smaller continents over 250 million years ago during the Mesozoic Era. It took millions of years for our continents to drift to their present locations. Wegener also accounted for their formation of mountain ranges. He suggested that as the continents moved, crust became crumpled in some areas. These areas became mountain ranges, like the Andes in South America.3 Wegener's continental drift hypothesis was cutting edge for its time. He had three types of evidence to support his hypothesis. Wegener looked at fossils found in Africa and South America. He believed that if continents were joined, then fossils of the same plants and animals should be on both continents. He gave the example of the Mesosaurus, which is a small, extinct land reptile. Fossils of this reptile have been found in South America and in western Africa. Scientists have dated the Mesosaurus fossils as part of the Paleozoic Era, over 270 million years ago. The two continents had to be joined for the fossils to exist in both places. Wegener also did not find evidence of land bridges that connected South America and Africa across the Atlantic Ocean.4 Wegener also studied rock formations. He found that rocks along the coastal regions of these separated continents matched closely in type and age. He proposed that mountain chains which began on one continent appeared to continue onto other continents across the ocean. For example, the Appalachian Mountains, located along the eastern coast of North America, appear to be similar in age and structure to the mountain ranges found in Greenland and Scotland. Wegener believed that if you put our continents together, the mountain ranges similar in age would fit together to form a continuous chain.5 The last type of evidence used by Wegener was changes in climatic patterns. He pointed out that geologists found evidence of glaciers in southern Africa and South America. Today these continents are too warm to support glaciers. Scientists have also found fossils of plants that would normally grow in tropical or subtropical areas, in areas that have colder climates. Continents that were once joined together would have been located in areas that resulted in climates different from today.